Adrian Lock, Met Office, UK Boundary layer scheme development - - PowerPoint PPT Presentation

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Feb 14, 2023 244 likes •383 views

Adrian Lock, Met Office, UK Boundary layer scheme development arising from EUROCS stratocumulus simulation Convection scheme development spawned by shallow cumulus simulation Boundary layer scheme plus development 1 st order

SLIDE 1

Adrian Lock, Met Office, UK

Boundary layer scheme development

arising from EUROCS stratocumulus simulation

Convection scheme development

spawned by shallow cumulus simulation

SLIDE 2

Boundary layer scheme plus development

1st order specified K-profile closure

Diagnose vertical extent of K-profiles by imposing a

limit on the buoyancy consumption of TKE, using subgrid cloud-base height diagnosis: With D=0.1 taken from the LES of the diurnal cycle

f marine stratocumulus

' ' ' '

i i

z z

w b dz D w b dz

SLIDE 3

SCM stratocumulus: decoupled phase (11Z local time)

Inversion

K profiles Kh

top

Kh

surf

Cloud base

Buoyancy flux

If well-mixed Decoupled

l profile

SLIDE 4

Impact of the new subgrid cloud-base diagnosis JJA means

New method Old method Difference Occurrence of decoupling Total cloud fraction

SLIDE 5

Climate model cloud fraction – 5 year JJA mean

ISCCP New model

Old model (HADAM3) – ISCCP New model (HADGEM1) – ISCCP

SLIDE 6

Convection scheme plus developments

Gregory and Rowntree (1990) mass-flux scheme

(with RH-dependent CAPE closure for deep convection) plus:

Trigger at the LCL using explicit cumulus diagnosis

Cap K-profile at LCL

Shallow convection parametrized with:

Grant and Brown (1999) entrainment/detrainment rates mLCL = 0.03 w* parcel just saturated with wv LCL = - 0.2 wv S

SLIDE 7

Parcel perturbation gives warmer/drier sub-cloud layer Larger entrainment/detrainment rates give

Colder and moister cloud layer Lower cloud top

Profiles at end of simulation

Revised Original Original Revised

SLIDE 8

Same warmer/drier

sub-cloud layer

Same colder and

moister cloud layer

Same lower cloud top

Cross-section 1, July mean, New – Old

Theta Humidity

SLIDE 9

Revised Original

SLIDE 10

Cloud-top lower but

little impact on cloud cover except towards the ITCZ

SLIDE 11

Original Revised

Massflux time-height sections from a point near Hawaii

Partly a more robust trigger, partly more balanced increments...

SLIDE 12

NWP representation of stratocumulus (T+12)

Old NWP model (Ri bl scheme) New NWP model (non-local bl scheme) Radiosonde ascent

SLIDE 13

Both K-profile boundary layer and revised

convection schemes are now operational for NWP

Further work required on the interaction between

cumulus and stratocumulus

Extend the principle of K-profile mixing between

layer interfaces to:

cumulus convection (both shallow and deep) stable boundary layers